Hydraulic servosystem



May 27, 1969 D. c. HOWLAND HYDRAULIC SERVOSYSTEM Filed May 12, 1966FIG.2

m WW w mfi 5 w w W F United States Patent U.S. C]. 137-85 ClaimsABSTRACT OF THE DISCLOSURE This is an improved hydraulic servosystemwherein relatively small changes in electrical current flow through anelectromagnetic operator effects predetermined accurate changes in thecontrol function of a flow control device.

It is characterized by requiring the fluid controlled by the valvemember to flow around such member prior to its entering the flow controlorifice. More specifically, the source of fluid pressure is so orientedwith respect to the valve or flow control member that the flow of fluidis not in opposition to the magnetic force attempting to locate theprecise position of the flow control member but rather is additive tosuch magnetic force. Thus, the valve member is upsteam of the flowcontrol orifice.

The present invention relates generally to hydraulic servosystems, andmore particularly to such systems which exhibit improved operatingcharacteristics.

Hydraulic servosystems are used extensively today for controlling theoperation of many different instrumentalities. Such systems areparticularly useful in conjunction with electrical operating meanswhereby variations in electrical current flow can be used to controlrelatively large physical movements as effected by the hydraulic system.

Hydraulic servosystems in the broadest definition, are not new today,but many of the prior systems have not operated satisfactorily forvarious reasons. One particular shortcoming of prior systems has beenthe inability to respond to very small changes in electrical currentflow. T hat is, under certain conditions, it is desirable, if notmandatory, to have a pressure responsive element such as a piston,respond to very small changes in current flow.

The electroresponsive actuator used in such cases usually comprises anelectromagnetic operator such that the magnetic polarization is variedto' provide the different control conditions. In attempting to alleviatethe above-mentioned shortcomings, improvements have been made in theelectromagnetic operators, such as by utilizing resistance free mountingmeans for the armature so that it will respond to extremely smallchanges in magnetic flux as accompanies a very small change in controlcurrent applied to such operator. However, in spite of the various priorimprovements that have been attempted, there has heretofore existed alimitation regarding the minimum amount of current variation that couldbe used to control a hydraulic servosystem. One reason for this has beenthe fact that the armature of the electromagnetic actuator has beenrequired, under certain circumstances, to work against the fluidpressure being controlled. This condition has not only requiredrelatively large forces to accomplish the desired work but has alsoresulted in a less efficient, less sensitive and less accurateservosystem.

It is an object of the present invention to provide a hydraulicservosystem which is considerably more efficient than prior systems inconverting a control energy into actual work.

3,446,229 Patented May 27, 1969 Another object of the present inventionis to provide a hydraulic servosystem as characterized above, whereinthe control force is not caused to act directly against the force of thehydraulic fluid.

Another object of the present invention is to provide a hydraulicservosystem as characterized above, which utilizes the force of thepressurized hydraulic fluid to advantage in assisting the controlfunction during the most critical periods of operation of theservosystem.

A still further object of the present invention is to provide ahydraulic servosystem as characterized above, wherein the direction offluid flow is reversed as compared to previous systems so that themovable control element is urged toward the control orifice by thepressure of the fluid which it is controlling.

A still further object of the present invention is to provide ahydraulic servosystem as characterized above which is simple andinexpensive to manufacture and which is rugged and dependable inoperation.

.The novel features which I consider characteristic of my invention areset forth with particularity in the appended claims. The device itself,however, both as to its organization and mode of operation, togetherwith additional objects and advantages thereof, will best be understoodfrom the following description of specific embodiments when read inconnection with the accompanying drawings, in which:

FIGURE 1 is a top plan view of a hydraulic servosystem according to thepresent invention;

FIGURE 2 is a sectional view of the system of FIG- URE 1, takensubstantially along line 2-2;

FIGURE 3 is a diagrammatic sectional view of certain portions of thesystem of FIGURE 1;

FIGURE 4 is a fragmentary sectional view of a control element andorifice of the present system; and

FIGURE 5 is a graph of certain characteristics of previous systems asWell as the present invention.

Like reference characters indicate corresponding parts throughout theseveral views of the drawings.

Referring to FIGURE 1 of the drawings, there is shown therein aservosystem according to the present invention contained within ahousing identified generally with the numeral 10. Such housing, as shownmore particularly in FIGURE 2, is formed of several housing memberswhich are held together by any appropriate fastening means such as bolts12. Y I

The subject servosystem comprises generally an electromagnetic actuator14, a hydraulic actuator 16, slide valve 18 and a pressure responsiveelement or slave valve 20. These parts cooperate in a manner not unlikeservosystems heretofore available, but difler therefrom by the manner inwhich the fluid flow to the slave valveis controlled, as willhereinafter become apparent to those persons skilled in the art.

The electromagnetic actuator 14 comprises an electromagnetic nnit 22which includes one or more windings, shown schematically in FIGURE 3 at24 and 26, andsuitable magnetic core means 28. As is well-known in theart, such electromagnetic actuator is frequently termed a torque motorand responds to changes in electrical enorgy in the windings 24 and 26to create changes in magnetic flux flow along predetermined paths. Suchflux flow is operable to attract an armature 30in opposite directions aswill hereinafter be explained in greater detail.

The armature of the present embodiment is formed integrally with acontrol element 32, the resulting combination being termed anarmature-control element throughout the description and claims.

As shown most clearly in FIGURE 2 of the drawings, electromagneticactuator 14 includes a frame member 34 which comprises a cylindricalhollow portion 34a. Such portion constitutes a housing for the armature30,

such armature being movable therewithin in accordance with theaforedescribed changes in magnetic flux afforded by the electromagneticunit 22. Frame member 34, of course, is firmly anchored to the otherhousing members as will be readily apparent to those persons skilled inthe art.

The armature-control element 32, as above described, may be formed as asingle unitary structure but is shown in the drawings as comprising twoseparate elements firmly attached together. Armature 30 is generallycylindrical in construction and is provided with an enlargedintermediate portion 30a and a reduced lower portion 30b. The latterportion is press-fitted within an opening formed in the control element32.

Element 32 is further formed with an annular flange 3211, a portion 32bof which is reduced in thickness to provide annular flexible mountingmeans. The peripheral portion of flange 32a is heavier and is firmlyfastened between suitable housing members so as to firmly anchor thearmature-control element in proper position. The relatively thin reducedannular portion 32b permits the armature 30 and the control element 32to pivot as a unit as will hereinafter become apparent.

Suitable pressure equalizing passageways 36 and 3-8 are provided withinthe armature 30, and a similar opening 40 is provided in the side ofcontrol element 32. The pressure within the armature-control element isthus caused to equal the pressure therewithout so that such fluidpressure in no way influences the position or movement of suchstructure.

The control element 32 is positioned within a fluid chamber 42 formovement between certain flow controlling positions. Such chamber 42 isformed between various housing members as shown in the drawings.

A pair of oppositely disposed orifice members 44 and 46 are positionedwithin the housing to extend within the fluid chamber 42. Such orificemembers are individually formed with control orifices 44a and 46a,respectively,

'the aforementioned placement of such orifice members thereby disposingsaid orifices in opposed relation as shown in FIGURES 2 and 3 of thedrawings. As will hereinafter be explained in greater detail, thecontrol element 32 is movable relative to and against each of saidorifices, alternatively, to control the flow of fluid therethrough.

Immediately beneath pressure chamber 42 as shown in FIGURE 2 of thedrawings, is a slide valve 48. Such valve comprises four annular controlportions 48a, 48b, 48c and 4811 which cooperate with various fluid portsformed in a cylinder or cylindrical housing for said valve. The fluidports are shown in FIGURE 2 at 50, 52, 54, 56, 58, 60 and 62, the ports50 and 56 having both upper and lower portions in the cylinder as shownin FIGURE 2.

Each of the fluid ports in the cylinder cooperates with a separate oneof the annular control portions of the slide valve 48, and is connectedto one or more passageways.

For communication with ports 52 and 54 there is provided a source offluid pressure '64 which may take substantially any desired form. Inlike manner, there is associated with each of ports '50 and 56 suitblereservoirs 66 and 68, respectively.

The slave element shown in the lower portion of FIGURE 2, may takesubstantially any desired form. For instance, the piston 70 may beemployed to respond to changes in fluid pressure in chambers 72 and 74.That is, if the pressure in chamber 72 predominates, such piston 70 ismoved to the left, and conversely, if the pressure in chamber 74predominates, the piston 70 is moved to the right. As will be readilyapparent to those persons skilled in the art, the slave unit 20 shown inthe drawings is primarily for purposes of illustration, it beingunderstood that corresponding equipment or instrumentalities might beutilized which p oduces the same or similar response to the operation ofthe electromagnetic actuator. The chambers 72 and 74 are provided withfluid flow through conduits 76 and 7-8 respectively which receive fluidunder pressure from the orifice members 46 and 44, respectively, in awell known manner. A reservoir or accumulator 79 is provided forrelieving the pressure at one end of the piston 70 when the latter iscaused to move in response to increased pressure at the other endthereof.

Referring to the schematic showing in FIGURE 3 of the drawings, theoperation of the subject invention will now be explained. As is wellunderstood, the armature 30 is pivoted to the left or right as viewed inthis figure in accordance with the energization of either or both of thewindings 24 and 26. The direction of current flow in such windings aswell as the amount of such current flow determines the amount anddirection of flux flow which results. Accordingly, the armature 30 isattracted to either the right or the left.

The relatively thin disk like mounting means 32b enables such armatureto be pivoted in response to small magnetic flux flow by such windings.As said armature pivots, of course, the flow control element 32 iscaused to approach one or the other of the orifices 44a and 46a. In theevent such armature is moved to the left, as viewed in FIGURE 3, suchflow control element approaches the orifice 46a. Conversely, if thearmature 30 is moved to the right, the control element approaches theorifice 44a.

Initially, the source of fluid pressure 64 provides fluid pressurewithin the chamber 42. Such pressure results in fluid flow from chamber42 through both of the orifices 44a and 46a as well as orifice members44 and 46.

When the armature 30 is attracted to one position or the other, thecontrol element is moved into a flow restricting position with respectto one of the orifices 44a and 46a. Such flow of fluid has considerableeffect upon the action of the control element 32 as it cooperates withthe respective orifice due to the fact that the path around such elementis restricted.

Heretofore, such fluid flow has been in the direction from therespective orifice member into the pressure chamber 42, such priorsystems having the source of fluid pressure So associated with theseveral orifice members.

As shown in FIGURE 4 of the drawings, the projection of the orifice onthe control element 32 provides an indication of the path of fluid flowin prior devices from the orifice to and against the side of the controlelement 32. Such fluid flow resulted in the application of a force tothe control element, which force constituted a spring effect whichworked against the control action of the control element in movingtoward the orifice. That is, in attempting to restrict the flow of fluidfrom an orifice toward the control element, the control element wasrequired to generate suflicient additional force to overcome the dynamiccharacteristics of the moving fluid.

In designing servosystems of such prior construction, it was necessaryfor such spring effect which was calculable as a constant to be takeninto account in evaluating the various physical and functionalproperties of the electromagnetic actuator associated therewith.

With the present invention the flow of such fluid is from the chamber42, around the control element 32 and then through the respectiveorifice. The net effect of this arrangement is that the spring effect isin the direction of movement of the control element 32. This means thata smaller electromagnetic actuator can be employed and the resultingsystem is considerably more efiicient and sensitive, and is easier todesign. Also, it has been found that the system according to the presentinvention is more reliable and is less expensive to manufacture.

A diagrammatic showing of the improved operational characteristics isshown in FIGURE 5 of the drawings. The curve 80 therein shows for priorsystems the relationship between the amount of current flow in theelectromagnetic actuator necessary to effect predetermined change inpressure as applied to the slave element. The curve 82 shows the samesuch relationship but as derived from a system according to the instantinvention. It will be noted from these curves that whereas a relativelylarge change in current flow is necessary with prior devices to effect apredetermined change in pressure on the slave element, the presentinvention is such that only a small current flow is required toaccomplish the same work.

Additionally, such new design increases the sensitivity and accuracy ofthe resulting servo system due to the cooperative nature of the fluidpressure and the electromagnetic forces as applied to control element32.

As will be readily apparent to those persons skilled in the art, theother portions of the servosystem are in accordance with priorteachings. The movement of control element 32 also changes the positionof slide valve 48 within the cylinder thereof. This results inappropriate control function of the various ports along such cylinder sothat fluid under pressure is appropriately applied to the slave piston70. Also, such control function results in the opening of certain bleedports so that the pressure on the opposite side of the slave piston isrelieved.

It should also be realized that the action of slide valve 48 controlsthe application of fluid pressure to the chamber 42 as above mentioned.The position of annular control elements 48b and 480 of slide valve 48with respect to the respective ports 52 and 54 controls the flow offluid under pressure from source 64 to such chamber. Such operation,however, is part of the overall servosys tern as is well understood inthe art.

It is thus seen that the present invention provides a unique servosystemwhich is considerably more accurate, reliable and sensitive as comparedto prior systems. Also, the present system is capable of operatingproperly in response to very small changes in current flow.

I claim:

1. In an electromagnetic servo valve the combination of, means forming afluid chamber having a wall formed with an orifice, an electromagneticactuator comprising electrically energizable means and an armature to bemoved in accordance with energization thereof, a flappertype flowcontrol element within said chamber formed integrally with said armatureto provide a unitary structure therewith to move relative to saidorifice in response to movement of said armature, and means affordingfluid pressure to said chamber causing said orifice to be downstream ofsaid flow control element whereby said element is substantially immuneto variations in the physical characteristics of the fluid caused bypassage thereof through said orifice.

2. The invention defined in claim 1, wherein a valve body is providedwith an enclosure for said armature, and pivotal mounting means isprovided for said unitary armature and flow control element.

3. The invention defined in claim 2, wherein said electromagneticactuator comprises an electromagnetic winding about said enclosure toattract and repel said armature to position accordingly said flowcontrol element relative to said orifice.

4. The invention defined in claim 3, wherein substantially linearbiasing means is provided between said valve body and said unitaryarmature and flow control element to act in opposition to the attractionand repulsion of said electromagnetic actuator to thereby cause theposition of said flow control element to be infinitely variable withinpredetermined limits relative to said orifice.

5. In an electromagnetic servo valve the combination of, means forming afluid chamber having two walls each of which is formed with an orifice,an electromagnetic actuator comprising an electromagnetic winding and anarmature to be magnetically attracted and repelled, a flapper-type flowcontrol element within said chamber formed integrally with said armatureto provide a unitary structure therewith for reverse movement relativeto said orifices in response to movement of said armature, substantiallylinear biasing support means for said unitary structure, and meansaffording fluid pressure to said chamber causing each of said orificesto be downstream of said flow control element whereby said element issubstantially immune to variations in the physical characteristics ofthe fluid caused by passage thereof through either of said orifices.

References Cited

